Pulpstone



y 1937- H. w. H. BETH 2,079,787

PULPSTONE Filed Aug. 12, 1936 Hu o W H. BETH Gum,

Patented May 11, 1937 UNITED STATS PAT T FFICE PULPSTONE tion of Massachusetts Application August 12, 1936, Serial No. 95,503

4 Claims.

The invention relates to pulpstones.

One object of the invention is to provide an improvement in the type of pulpstone disclosed in United States Letters Patent Reissue No.

5 19,678 to R. C. Benner and H. E. Stowell. Another object of the invention is to avoid fracturing of the sectors of a pulpstone by reason of differential thermal expansion thereof. Another object of the invention is to provide an ef- 1 ficient construction for a pulpstone. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, as will be exemplified in the structure to be hereinafter described and the scope of the application of which will. be pointed out in the following claims.

In, the accompanying drawing, the single figure thereof represents an axial sectional View of one-half of a pulpstone constructed in accordance with the invention, together with the mounting shaft and flanges.

In the illustrative embodiment of the invention I provide a pulpstone construction which,

with the exception of the feature to be specifically pointed out hereinafter, may be substantially the same as that disclosed in the Reissue Patent No. 19,678 to Benner and Stowell above referred to. For example, I may provide an outer body or annulus l of abrasive annuli 2 each one of which comprises a plurality of sectors. I may further provide an inner portion 3 of concrete or other material as disclosed in the aforesaid Bennor and Stowell patent. I may further provide driving flanges 5 in threaded engagement with a driving shaft 6 and I may provide a pair of metal facings ill.

I may further provide reinforcing rings or hoops 8 such as disclosed in U. 8. Letters Patent to Bonner and Soley No. 1,975,970. These may be surrounded with material 9 of any of the formulae disclosed in the patent last above identified- I may use any other features in either of the twopatents mentioned not inconsistent with each other, and the accompanying drawing clearly discloses the illustrative embodiment of this invention so far as constructional features are concerned.

Pulpstones constructed in accordance with the patents above identified have been found in actual practice frequently to fail in service by the fracturing of one or more end sectors of the annuli identified in the accompanying drawing by the references 2a. I have found that this occurs despite careful balancing or attempts at balancing coeificients of expansion, for the reason that some portion of the abrasive annulus I is rigidly held between the flanges 5, 5 while the outer portion of the abrasive annulus l is free to expand, and moreover the heat generated during grinding is generated at the periphery of the wheel and there is, during grinding, a thermal differential in the annulus I from the peripheral outside to the inner portion. It is probably true 1 that no metal parts of the shape of the flanges 5 can resist a direct thrust due to thermal expansion. Nevertheless, the pressure of the flanges 5 is a factor insomuch as axial expansion of the outer portion of the annulus I would otherwise force axial expansion of the inner portion, even though cold, by reason of the integral connection. While the flanges 5, 5 might not be able to resist a direct thrust from thermal axial expansion of the inner portion of the abrasive annulus I, they can resist axial expansion of this inner portion of the annulus (inside the rings 8) by reason of thermal expansion of the outside portion of the annulus (outside of the rings 8) because this force can be no greater 25 than the shearing strength of the abrasive annuli which is weakened at what I term the throats, H.

As partly explained .in the patents referred to, there is great force exerted by the flanges 5 upon the pulpstone in an axial direction. This is 30 due to the right and left-hand threads on the shaft 6 which are so disposed, with relation to the direction of rotation, that rotation of the pulpstone and consequent resistance due to grinding at the periphery tends to tighten the flanges 5. A pulpstone may, when it is started up, be quite cold. As it is started, the full load is placed upon the annulus l and this tends to tighten the flanges 5 on the shaft 6, the shaft 6 being at that time cold. The periphery of the annulus I heats up first and becomes quite hot even down to the rings 8 while the rest of the stone, including the flanges 5 and the shaft 6, may still be quite cold. It will be understood that conditions met with in practice vary considerably and 45 the foregoing is a conservative statement of what happens when a pulpstone is started and, for one reason or another, the water gives out soon after the start of the grinding operation. Under such conditions, temperatures way above the boiling point of water may be reached and transmitted to the entire outer portion of the annulus i.

As the annuli 2 and 2a, are heated, those annuli at the center or near the center do not first fracture, as the pressure is more or less the same on both sides. The worst condition is met with at the annuli 2a. and, therefore, in actual practice, these are usually the first to go. It will be seen that the annuli 20., so far as the outer portion outside of the rings 8 is concerned, are absolutely unsupported, on the outside (in an axial direction) while from the inside (in an axial direc tion) they are subjected to the sum of the exl0 pansions due to the coeifioient of expansion of the material times the number of degrees of temperature differential times the axial length of the annulus 1 inside the outside annuli 2a. As these same annuli 2a are rigidly held inside of the rings 8, a leverage is produced which frequently fractures them.

I correct this condition by providing compressible fillers I2. Preferably I use a material different from that disclosed for the embedding material 9 in Patent No. 1,975,070. This filler material I2 need not have any function so far as holding the sectors together in an axial direction is concerned. This function is sufficiently achieved by the construction otherwise disclosed and disclosed in the patents referred to. While it is sufficient, so far as conditions usually met with in practice are concerned, to provide fillers I2 which have the shape of annular disks, or

' sectors thereof, I may also provide fillers between sector blocks in a circumferential direction, as indicated by the reference character I3 at" the central portion of the annulus I. The

Single figure will be understood to be an axial sectional view of the embodiment of the invention in which both types of fillers are used, disclosing fillers I3 which extend in axial planes at the central portion of the drawing, the section plane being broken. In the preferred embodiment of the invention both the annular fillers I2 and the axial fillers I3 will be provided, but so far as certain features of the invention are concerned and under certain conditions of operation only the fillers I2 will be used.

It will be understood that so far as practical requirements are concerned, it is sufficient to safeguard the pulpstone against certain stresses and expansions without safeguarding it against all. In fact, considering each abrasive sector as a unit, if the outer portion be heated up and the inner portion be not heated, there is a certain strain set up in the sector itself which no amount of mechanical device outside of the sector possibly could completely overcome. Nevertheless, abrasive material is sufficiently elastic to withstand a certain amount of such strain. It is the unsupported and multiplied strain and stress due to difierential expansion as hereinabove explained which this invention relieves.

Considering now the material for the fillers I2 and I3,.I prefer to use a compressible and deformable composition. One example of a composition which might be used is as follows:

Percent by weight Rubber 45.6

Sulphur 24.6 80 grit size silicon carbide 4.8

16 grit size cork 25.0

The above formula may be widely varied. For example, the following may be used:

Other materials for the fillers I2 and I3 may be used. For example, a Babbitt metal filler with compressible posts made according to the disclosure of United States Letters Patent No. 1,815,108 to Larsson may be substituted. The function of the fillers I2 and I3 is to deform under pressure, whether or not these fillers return to their initial condition after the particular stress or strain has been relieved and the stone returns to a state of thermal equilibrium.

In the drawing I have shown the flanges 5 and the metal facings I0 as slightly larger in diameter than in the reissue patent to Benner and Stowell above referred to in so much as, due to the provision of the compressible fillers I2 and I3, the flanges 5 may be extended outwardly and by doing. so differential strains if the heat ever penetrates to the interior portion of the annulus I are better avoided. By extending the metal parts further outwardly, a directthrust which will deform the metal is achieved by the thermal expansion and this to some extent reduces what I term the leverage effect of the expansion. This leverage effect is due to holding the material at the inside and providing a condition where thermal expansion creates a turning couple at the outside of the annulus. There is a certain resiliency to the material 9 which sufiiciently overcomes the leverage effect so that the construction illustrated in the drawing fulfills practical requirements. However, so far as many features of the invention are concerned, the flanges 5 have the same relation to the abrasive annulus I as is disclosed in the aforesaid patent to Benner and Stowell.

The joints into which the fillers I2 and I3 are placed may be of the order of a quarter of an inch wide. With the use of a different filler material, spaces of different width may be provided. I may provide abrasive segments of zigzag contour in developed view, as disclosed in U. S. Letters Patent No. 1,469,723 to Greenwood, but on the other hand due to the narrowness of the fillers I2 and the fact that there is some abrasive grain in the composition, the faces of the sectors may be in radial planes perpendicular to the axis.

Considering now the manufacture of the entire pulpstone, it may be assembled according to previous practice, laying the filler material I2 and I3 in position as the sectors are assembled. Then by means of a single heat treating operation, the fillers I2 and I3 as well as the material 9 may be vulcanized, and at this same time other material which is thermally set in accordance with the disclosure of the patents to Benner and Stowell and Benner and Soley may be heat treated. Other procedures currently in use or which may be adapted to the circumstances may be employed in the assembly and construction of the stone.

It will thus be seen that there has been provided by this invention an article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a pulpstone construction, a shaft having right and left-hand threads, flanges mounted on the shaft in threaded engagement with said threads, an inner portion to the stone extending around the shaft and radially smaller than the flanges so that the pressure of the flanges may be exerted beyond the inner portion, sectors arranged in the form of an annulus and around the inner portion, reinforcing rings embedded in the sectors, the sectors abutting each other in an axial direction inside of the rings and at that portion receiving the thrust of the flanges, and fillers of material which Will deform under pressure between the sectors, from end to end of the stone, outside of the rings.

2. In a pulpstone construction, a central support, a series of abrasive annuli each comprising a plurality of sectors mounted on said support, inner portions of said sectors being in abutting engagement axially, and outer portions of said sectors being spaced, and compressible fillers between said outer portions.

3. In a pulpstone, a central support, a series of abrasive annuli on said support, each annulus comprising a plurality of separate blocks, each block being in part at least substantially a sector and each block being wider in an axial direction at the inside adjacent the support than at the outside adjacent the periphery, means holding the blocks together axially, and means holding the blocks on the support radially.

4. In a pulpstone, a central concrete support, a series of annuli of abrasive blocks on said support together forming an abrasive annulus, each of the series comprising substantially sectoral blocks, and metal rings between individual annuli of the series of annuli, the blocks being in non-compressible relation inside the rings, and the blocks being spaced outside the rings.

HUGO W. H. BETH. 

